Comparing Winter Snowfall with ENSO Phase
The work that Eric Webb (@webberweather) has been doing to create an ensemble from numerous ENSO (El Nino/Southern Oscillation) data sets has yielded the chart below which shows his “best guess” ENSO phase for each winter season dating back to 1865.
Among other things, this list allows for easy comparison of ENSO phase with other variables measured on seasonal time scales. One interesting comparison is with seasonal snowfall for some eastern US cities. Here are a few examples by region:
(Image Credit: Ian Livingston)
(Image Credit: Eric Webber)
What can these charts tell us?
It is possible to draw some very general conclusions from these charts. For a strong El Nino year like 2015-16 you could say that the southeast is favored for above normal snowfall while odds tilt towards below normal snowfall for the mid-Atlantic and northeast. There are a few things to keep in mind though. First, these cities may not be representative of the broader region to which they belong because of geographic factors such as elevation or proximity to water. Also, for strong El Nino/La Nina years the sample size is much smaller than the more moderate or neutral phases increasing uncertainty during those regimes. Most importantly the behavior of the atmosphere is extremely complex and never driven solely by one factor. It's almost never a good idea to rely on one variable when forecasting or assessing the weather especially on seasonal time scales..
One other notable fact that does not appear on the graphs above is that a wide range of seasonal snowfall amounts were observed among all ENSO phases for the cities considered. The NYC graph included below includes bars depicting the ranges of values that were used to determine the average snowfall during each ENSO regime.
So while the odds may favor below average snowfall during stronger El Nino years in NYC or Boston, a strong El Nino does not guarantee below normal snowfall. A forecaster would need to consider the correlation between ENSO phase and seasonal snowfall in its proper context- as one piece in a very complicated puzzle.
Without a more thorough review consisting of numerous cities within well-defined regions it is wise not to draw too many conclusions from these charts alone. However, there are regional impacts of ENSO phase on snowfall in the eastern US (and elsewhere) that have been documented in peer-reviewed studies such as this one.